2017 ASHS Annual Conference

Groundwater depletion is a serious problem in California, where up to 60% of the annual water supply can come from groundwater during drought years. As underground reservoirs are being depleted at an unsustainable pace, agricultural lands are being looked at as potential sites where excess winter water can be used to recharge groundwater. Almond orchards cover 1.1 million acres, predominantly in the Central Valley. An estimated 675,000 acres may be moderately suitable for recharge from a water movement perspective, however, tree health impacts of using this land for water recharge are unknown. Two central Valley and one northern Valley orchards with mature trees were exposed to winter flooding in January 2016 (two central suites) and 2017 (all three sites). In 2016 and 2017, the central sites received an additional 24” (61 cm) of water, while the northern site, which has much less permeable soil received an additional 4” (10 cm) of water in 2017. Root observation tubes were installed to track root production and death, and trees were monitored for bloom data, stem water potential, twig carbohydrate content (starting Fall 2016) and yield. Preliminary data show few impacts of the treatments on stem water potential, twig carbohydrate content and yield. Root production was marginally greater in the block used for recharge at the most sandy site, however this effect was likely confounded by a slight change in soil characteristics across the site. As two of the sites suffer from a lack of replication, a comparison between the 2016 data (a normal year) and the 2017 data (wettest year on record) will help determine the range of possible positive and negative impacts of winter recharge.